In situ hybridization showed that mouse homeobox NKx-1.2 mRNA is present in postmeiotic germ cells of the testes and in discrete areas of the adult brain. One species of NKx-1.2 mRNA is present in mature spermatozoa from the mouse epididymis. Ten NKx-1.2 cDNA clones were sequenced that correspond to four species of NKx-1.2 mRNA that are formed by alternative splicing at conventional 5-donor and 3-acceptor splice sites. In addition, seven cDNA clones were sequenced that correspond to species of NKx-1.2 mRNA that have novel 5- and 3-splice sites. Predicted amino acid sequences show that some transcripts may be translated into proteins that lack part of or all of the homeodomain. Targeted deletion of part of the NKx-1.2 gene was obtained by homologous recombination. Characterization of the phenotype of homozygous mutants is in progress. OG-9 is a paired-like homeobox gene from the mouse previously discovered in this laboratory. Northern analysis revealed OG-9 expression in RNA from brain, skin, ovary, and liver of adult mice and in late stage embryos. Sequence analysis showed that the OG-9 gene has three exons, two alternative polyadenylation sites, and several putative transcriptional start sites. The OG-9 gene was mapped to mouse chromosome 11, near the Evi2 locus. In situ hybridization of adult brain sections showed that OG-9 is expressed in the cingulate cortex, CA areas of the hippocampus, and the cerebellum. High levels of OG-9 RNA were detected in maturing oocytes and fertilized eggs; lower levels were found in the 2-cell embryo, but none was detected in 4-8 cell embryos. Hence, OG-9 is a maternally expressed homeobox gene. - homeobox gene, embryo, brain, testes, mouse, development